FORT MEADE, Md. -- The U.S. Army private accused of providing diplomatic cables and other secret documents to the WikiLeaks website pleaded guilty on Thursday to misusing classified material, but denied the most serious charge in the case, aiding the enemy.

Private First Class Bradley Manning, 25, entered the pleas prior to his court martial, which is set to begin on June 3, in a case that centers on the biggest leak of government secrets in U.S. history.

"I believe that if the general public... had access to the information... this could spark a domestic debate as to the role of the military and foreign policy in general," Manning, dressed in full military uniform, testified calmly.

FILE - In this June 25, 2012 file photo, Army Pfc. Bradley Manning, right, is escorted out of a courthouse in Fort Meade, Md. The Army private charged in the largest leak of classified material in U.S. history says he sent the material to WikiLeaks to enlighten the public about American foreign and military policy on Thursday, Feb. 28, 2013. (AP Photo/Patrick Semansky, File)
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Patrick Semansky
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Manning pleaded not guilty to the most serious charge, aiding the enemy, through his attorney. Manning, who has been jailed at Quantico Marine Base in Virginia for more than 1,000 days, could face life imprisonment if convicted of that charge.

He pleaded guilty to a series of 10 lesser charges that he misused classified information at the hearing before military judge Colonel Denise Lind. He faces a maximum of 20 years in prison for those charges.

He also admitted to misuse of documents from the U.S. Southern Command pertaining to Guantanamo Bay, a memo from an unnamed intelligence agency, and records from a military operation in Farah province in Afghanistan.

Manning, an Army intelligence officer, was arrested in May 2010 while serving in Iraq and charged with downloading thousands of intelligence documents, diplomatic cables and combat videos and forwarding them to WikiLeaks.

WikiLeaks began exposing the U.S. government secrets in the same year, stunning diplomats around the world and outraging U.S. officials who said damage to national security from the leaks endangered U.S. lives.

WikiLeaks founder Julian Assange has taken refuge in the Ecuadorean Embassy in London since June to avoid extradition to Sweden for alleged sex crimes.

Manning had offered to plead guilty to various lesser charges in violation of the Uniform Code of Military Justice, including the unauthorized possession and willful distribution of information accessed in the Combined Information Data Networks, a military database, for Iraq and Afghanistan.

He is prepared to take the witness stand to read aloud from a 35-page statement defending himself in the espionage case, but only after Lind rules on how much of it he will be allowed to read.

Under a ruling last month by Lind, Manning would have any sentence reduced by 112 days to compensate for the markedly harsh treatment he received during his confinement. While at Quantico, Manning was placed in solitary confinement for up to 23 hours a day with guards checking on him every few minutes.